Extended Childhood: a recent development

"Teeth are remarkable time recorders, capturing each day of growth much like rings in trees reveal yearly progress," says Tanya M. Smith, assistant professor of human evolutionary biology at Harvard.
"Even more impressive is the fact that our first molars contain a tiny 'birth certificate,' and finding this birth line allows scientists to calculate exactly how old a juvenile was when it died."

It had been found that the rate of growth of Neanderthal teeth was significantly faster than those of modern humans, even those humans that left Africa 100 000 years ago. As the growth rate of teeth is used to map overall development, this indicates that the extension of childhood is a relatively new development in hominids.

Humans' extended maturation may have allowed additional learning and complex  perception, possibly giving early Homo sapiens an advantage over their Neanderthal cousins